Charles Edmund Cullen
Cullen worked as a nurse in many hospitals but kept switching jobs as he was fired for suspicious behaviour from many of them. He confessed to murdering 40 elderly patients in New Jersey from 1984 to 2003. He did this by poisoning his patients to death with unprescribed medication. He stated that he wanted to relieve the patients from their suffering much like an angel would. Experts say he had more than 300 victims. Cullen has been imprisoned for life.